Last week, U.S. Senate majority leader Mitch McConnell urged governors to defy new federal regulations aimed at regulating the greenhouse gas emissions from power plants.

These regulations are designed to reduce national CO2 emissions 26 percent below 2005 levels by 2020, and 30 percent by 2030. This isn’t enough to stop climate change, but it’s an important step in the direction of a renewable energy economy.

Some do though. The worlds leading body of scientists studying climate change is called the IPCC. Last year, the IPCC issued it’s fifth assessment of climate change causes, risks and impacts.

That report is called the Fifth Assessment Report, or AR5. Some findings from AR5 include:

Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems.

Observed changes in the climate system Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.

Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks.

Surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level to rise.

Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread, and irreversible impacts globally.

So in deciding how to act, we have to choose. Between the world’s leading scientists, or people like McConnell.

When it comes to mitigation options, a couple of professors (Jacobson and Delucchi) from Stanford and UC Davis have documented how we could power the world’s economy on renewable energy at comparable cost to the current energy infrastructure. They state:

We suggest producing all new energy with WWS by 2030 and replacing the pre-existing energy by 2050. Barriers to the plan are primarily social and political, not technological or economic. The energy cost in a WWS world should be similar to that today.